1. Field of the Invention
The present invention relates generally to magnetic disk data storage media and more particularly to disk data storage media which contain uncopyable sequences of encoded data.
2. Description of the Prior Art
Personal or microcomputers are increasingly employed in a variety of applications in the home, business, scientific and educational environments. Typically, such computers store data on and retrieve data from disk storage media. Flexible disk storage media are most commonly used in conjunction with such microcomputers, although hard disk media may be employed as well. Designing, manufacturing and marketing of applications software, written onto such disks, is a major industry, accounting for millions o dollars in sales annually. Manufacturers expend substantial sums of money on the development of such programs, often only to see them copied by unauthorized "pirates". Further, particular disks produced in-house containing proprietary, confidential or otherwise sensitive information may require copy protection and/or permanent identification.
Various means of protecting and/or identifying certain types of information stored on various types of storage media are known in the art. However, these means are generally complex and require special equipment or are not adaptable to flexible data storage disks, or both. U.S. Pat. No. 4,333,113 issued to Kalinowski describes a method for monitoring the reproduction of sound or audiovisual recordings by coding auxiliary information in a limited frequency range and superimposing it on the primary information. This method does not actually protect against copying the master because the master having the auxiliary information can be copied using ordinary duplication techniques. U.S. Pat. No. 4,325,089 issued to Itsu describes a method for safeguarding data which is merely a means of magnetically destroying the data upon attempts to gain unauthorized access. Such device has limited use as the data becomes unreadable to the intended user, as well as the unauthorized user, and requires that the data be maintained within the apparatus of the invention.
U.S. Pat. Nos. 4,086,634 and 4,040,099 issued to Cook both relate to a method and apparatus for detecting tape piracy by preparing the program source material to include preselected inaudible signals to indicate the origin of the material in a manner similar to Kalinowski or to produce unacceptable interference signals to spoil the copy. U.S. Pat. No. 3,551,608 issued to Balint describes a method and apparatus for recording a plurality of copies from a master audio sound track, and for checking the quality of the copies relative to the master.
U.S. Pat. No. 3,004,104 issued to Hembrooke discloses a method and apparatus for the identification of signals, in order to positively identify the origin thereof. Hembrooke, like much of the art, relies on encoding an inaudible signal in a narrow frequency band. U.K. Patent Application No. 2,055,501A, submitted by Edmunds discloses an apparatus specifically for the purpose of producing video tapes which cannot be copied on an ordinary video tape recorder.
Other methods to copyproof disks currently known in the art include the use of weak signal pulses to interfere with the nominal transitions encoded onto a data track. Such a technique has been disclosed by an article appearing in Electronics, Sept. 22, 1983, entitled "Disk-Drive Generated Pulses Foil Piracy". This technique requires special equipment to generate the weak pulses, and may not operate at all when used on a drive with automatic gain control. Attempts have been made to provide a disk with a permanent serial number for positive identification by using high-coercivity media and special recording apparatus. These have been unsuccessful thus far.
In view of the prior art, there remains a need for a method of electronically identifying magnetic data storage media, and for providing a simple, positive means to differentiate a copy of the data from the original whereby valuable information stored on the media may be safeguarded.